Also for large-sized vehicles such as a bus and a truck, a vehicle of the type that the operation of a clutch pedal is not needed by automatically controlling a mechanical clutch, that is, a vehicle having an automatic control device for the mechanical clutch is widely spread.
In such a vehicle, the clutch is connected by automatic control with no operation of the clutch pedal by a driver during start-up.
However, there are cases where abnormal vibration (so-called “clutch judder (clutch chatter)”) occurs when connecting the clutch by automatic control during start-up (at automatic start-up).
When such clutch judder occurs, it is feared that the driver may have a remarkably uncomfortable feeling and driver fatigue may be increased.
In addition, the clutch is not smoothly connected and thus there is a possibility that, it adversely affects the start-up of the vehicle.
Further, in a case where the clutch judder has occurred, it is feared that, a shock of clutch connection may be increased and there exists a possibility that goods loaded on a truck may be damaged with the shock.
In order to prevent the clutch judder in a vehicle having an automatic control device for a mechanical clutch, for example, a technology for performing control to bring a clutch disc into a “disconnected” state (a connection released state) coping with a variation amount of a speed of a counter shaft in a transmission during start-up is proposed (refer to Patent Literature 1).
Although such the prior art (Patent Literature 1) is useful for clutch judder prevention, it has such a problem that, there are cases where it becomes difficult for a driver who has a habit of making a stepping amount of an accelerator pedal constant during start-up to start, up the vehicle.
In addition in the above-mentioned prior art (Patent Literature 1), there exists such a problem that the driver has to pay attention to the way of stepping the accelerator pedal so as not to induce the clutch judder and thus he becomes excessively nervous during start-up, which may lead to an increase in driver fatigue.